The present invention relates to the field of magnetic disk media More specifically, the present invention relates to rigid disk media used in high-speed magnetic disk drive storage systems.
Magnetic disk drive storage systems are typically used in computer systems. Digital information is stored on magnetic disk media in concentric memory tracks. The storage takes place in the form of magnetic transitions within a disk media. In a hard disk drive the disk media is a platter rotatably mounted on a spindle which supports the platter. The rotation of the disk platter creates a thin cushion of air, or other gas such as helium, over the surface of the disk platter.
Typically, an actuator is provided proximate to the disk platter to support a transducer incorporated into read/write heads. The read/write heads transfer data to and from concentric tracks formatted into the surface of the media. The tracks are electronically divided into sectors allowing information to be stored and retrieved from a specific track and sector on the disk media. The thin cushion of air lifts the heads over the surface of the disk. Using the cushion of air as a low friction gas bearing, the heads xe2x80x9cflyxe2x80x9d over the disk media. The actuator positions the transducer head over a track as the media rotates. The head remains stationary over the selected track until the proper sector is positioned under the transducer by the rotating media. Once properly aligned, the transducer head causes the desired transitions in the magnetic disk media. The heads are then repositioned for the next transition.
The ability to maximize the storage of data on the disk is partially a function of the ability to fly the heads close to the surface of the disk, such that the dispersion of the interaction for each data transition point is minimized. Minimal dispersion translates into a higher density of magnetic transitions in the magnetic recording media. In addition a lower flying height lessens the distortion of signals sent to and from the read/write heads.
Current trends to increase the power and speed of computers, while at the same time reduce the size of the computer, make it desirable to increase the areal density of storage on disk media and decrease the time required to write or retrieve information. Areal density may be increased by increasing the number of bits of information stored per inch of media (BPI) and/or increasing the number of tracks per inch of media (TPI). Generally, this requires lower flying heights for the heads. However, irregularities in the disk surface can cause disruptions in the gas bearing and head crashes as the heads fly closer to the surface.
Read/write access speed can also be improved by increasing the rotational speed of the disk media. Amongst other effects, the increased rotational speed decreases the time required to wait for a desired sector to rotate into position after the head is positioned over the desired track. However, computer hard disk media are susceptible to flutter when rotated at high speeds. Flutter can cause head crashes and track mis-registration, offsetting the benefit of the increased speed.
Disk flutter is induced by airflow over a disk. As a disk rotates it causes disturbances in the atmosphere surrounding the disk. These disturbances exert pressure on the disk platter and cause the disk to vibrate or flutter. In order to decrease disk flutter, the flow disturbance must decrease, or the response of the disk platter to the disturbance must decrease. A disk with higher modulus substrates can be less susceptible to flutter. In addition a disk sealed in a partial vacuum or a lighter gas, such as helium, can be less susceptible to flutter.
Conventional hard disk media use aluminum substrates. Aluminum substrates have a relatively low modulus and are therefore more susceptible to flow disturbance. Ceramics, laminates or other high modulus materials can also be used as a substrate for disk platters. However, high modulus materials such as ceramic are very hard and difficult to machine to the requisite smoothness. Machining can greatly add to the cost of the component. Laminates require additional steps to manufacture.
Control of vibrational disturbance can also be accomplished by decreasing the rotational speed of the disk drive. Flutter resulting from disk rotation speed is typically a squared function. However, disk drives are increasingly required to have higher rotational speeds in order to meet the demands for faster access times. Therefore, reducing the rotational speed to contain flutter is not effective.
It is also not effective to increase the thickness of a disk substrate to reduce flutter. Platters with thicker substrates put additional mechanical stress on the drive mechanisms. This unwarranted stress can result in bearing failure and drive motor problems, therefore it is also not effective.
Another approach includes laminating a vibrational damping layer between two rigid plates which can also be used to address vibrational problems. Two half-thick rigid aluminum platters can be laminated with a layer of visco-elastic adhesive in between. The energy absorbing property of the laminate greatly reduces the effect of flow disturbance and thereby minimizes flutter. However, the laminated platter process makes it inherently difficult to control substrate flatness. In addition if the vibrational damping layer is not in intimate contact with both rigid platters, trapped moisture may cause problems in subsequent processes wherein heat is applied.
Therefore, there is a need for an easily manufactured rigid magnetic media with super-smooth surface finish as well as excellent vibration performance to meet high rotational speed requirements.
In general, a rigid disk drive media and method for improving surface smoothness and vibrational damping of a disk, such as a magnetic computer disk, are disclosed. According to one aspect a computer disk drive media includes a substrate with a planarized dielectric coating. The dielectric coating can be a viscous material coated on to a disk substrate to form a dielectric coating that fills in the gaps of the previously formed geometry. The coated surface can result in a profile with improved surface smoothness. Still further smoothing may be accomplished by polishing the surface of the dielectric coating. The coating process can be accomplished via spin coating, free flow coating, or dip coating. The appropriate form of coating will depend on the polymer formulation. The damping layer can provide improved vibrational control and increased smoothness as compared to the surface of the substrate.
Various implementations can include one or more of the following features. The disk drive media can include multiple dielectric coatings. In addition a magnetic ferrous coating can be applied over the dielectric coating. In some embodiments, the dielectric coating is applied to an upper and a lower surface of the substrate.
According to other aspects, the substrate can include aluminum, ceramic or other substances. In addition the dielectric coating can include a photopolymer. In another aspect the dielectric coating can be between 0.1 xcexcm and 10 xcexcm thick. In one embodiment the dielectric coating is polished with chemical mechanical polishing.
Implementations of the present invention can include a method for forming a computer disk drive platter with improved vibration control by applying a dielectric coating to a disk substrate. The vibrational damping material can be applied at a first grind stage, or other stage. In one embodiment, the dielectric material can be applied using a spin-on planarization technique including application of a polymer formulation to a surface of a substrate platter; spinning the substrate platter to form a uniform layer of the polymer formulation across the surface and curing the polymer formulation on the substrate.
According to another aspect, the method includes preheating the substrate. The method can also include curing being performed in a vacuum pumped chamber.
According to one embodiment the method disclosed can also include the step of baking the substrate platter with a layer of cured polymer formulation at a temperature of between 160xc2x0 C. and 200xc2x0 C. in addition to a nitrogen purge. In another embodiment, the method can include baking the substrate platter with cured polymer formulation at a temperature of between 170xc2x0 C. and 190xc2x0 C. under vacuum.
In still another embodiment this invention provides for a computer disk drive including a transducer supported by an actuator arm, the transducer can be located proximate to a media that is coated with a planarized magnetic means for providing viscous damping.